1. Field of the Invention
The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus capable of reading shading data.
2. Related Background Art
A film scanner for inputting the image of a film into a personal computer is so constructed that in the image reading operation, first scan the image with a low resolution and a high speed (pre-scan) is performed to thereby display the entire image on the personal computer, and then the main scanning operation in a desired range designated on the preview image is performed to thereby send the obtained image data to the personal computer.
The configuration of such film scanner will be explained in the following with reference to FIG. 28, in which shown are an illuminating light source 2801; a film holder 2802 for supporting a film constituting a translucent original and capable of transporting the thin translucent film, supported on the plane of the drawing (Y-Z plane), in a direction Y; an imaging lens system 2803; and a CCD linear image sensor 2804 (hereinafter simply called linear image sensor). The linear image sensor 2804 is positioned that its longitudinal direction is along a Z-direction in the plane of the drawing. By such arrangement, the main scanning direction, which is the longitudinal direction of the linear image sensor 2804, becomes perpendicular to the moving direction of the film holder 2802. In reading the color image on the film, there can be conceived following variations in the combination of the light source 2801 and the linear image sensor 2804:
These methods have respective advantages and disadvantages. In the following description, there will be assumed the combination (1).
In FIG. 28, there are shown an analog image processing circuit 2805 for gain setting and clamping of an analog image signal output from the linear image sensor 2804; an A/D converter 2806 for converting the analog signal into a digital signal; a digital image processing circuit 2807 for effecting image processing and CCD drive pulse removal; an image processing circuit 2807 composed of a gate array and capable of various high-speed processings; a line buffer 2808 for temporarily storing the output image data from the digital image processing circuit 2807; an interface 2809 for communication with an external equipment 2810 such as a personal computer; a system controller 2811 for releasing control signals based on a stored sequence program of the entire film scanner and adapted to execute various operations according to instruction from the external equipment 2810; a CPU bus 2812 connecting the digital image processing circuit 2807, the line buffer 2808 and the interface 2809 and composed of an address bus and a data bus; a sub scanning motor 2813 composed of a stepping motor for displacing the film holder 2802 in the sub scanning direction; a sub scanning motor driver 2814 for driving the sub scanning motor 2813 according to a command from the system controller 2811; sub scan position detecting unit 2815 composed of a photointerrupter for detecting a projection of the film holder 2802, for detecting a reference position of the sub scanning; and a light source activation circuit 2816 for activating the illuminating light source 2801.
The film scanner is constructed as explained in the foregoing, and is adapted to release image data to the external equipment 2810 according to a software of the system controller 2811 (hereinafter called xe2x80x9cfirmwarexe2x80x9d) and a software (hereinafter also called driver software) for operating the film scanner from the external equipment such as the personal computer 2810. The procedure will be explained briefly with reference to FIG. 29. It is assumed that the film scanner and the external equipment 2810 are powered, that the firmware and the driver software are activated and that the film has been loaded by the user in a predetermined position of the film holder 2802.
At first, in a step S2901, the user enters a preview command from the external equipment 2810, which in response provides, through the driver software, the firmware with the designated information, including the kind of the film, the reading area (entire image area in this case) and the reading resolution (low resolution).
In a next step S2902, the firmware sets the designated information, namely the film kind, the reading area and the reading resolution, on the system controller 2811, thereby effecting electrical preparation.
In a next step S2903, the sub scan position detecting unit 2815 read the information of the sub scanning position, and the system controller so controls the sub scanning motor 2813 as to bring the film to an initial position.
In a next step S2904, the system controller 2811 sends a command to turn on the light source to the light source activation circuit 2816, thereby turning on the light source 2801.
Then, in a step S2905, the system controller 2811 outputs a command for the output of timing pulses (driving pulses for the linear image sensor 2804, RAM address control pulses etc.) for the reading of a line.
A next step S2906 reads the image data of each line with a predetermined exposure time and drives the sub scanning motor 2813 with a predetermined speed. Thereafter the digital image processing circuit 2807 executes the image processing, and the image data are output to the external equipment 2810.
When the scanning of the above-mentioned image reading area is completed in a step S2907, the system controller 2811 drives the sub scanning motor 2813 to return the film holder to the initial position. Also the light source 2801 is turned off, and various functions are terminated as soon as all the image data are output from the digital image processing circuit 2807.
A next step S2908 terminates the scanning, and the firmware of the system controller 2811 enters a routine for awaiting a next command.
In a next step S2909, the external equipment 2910 receives the image data and displays them in succession on a display or the like connected to the external equipment 2810, thereby providing the user with the entire image of the film.
Then, in a step S2910, the user observes the displayed preview image, then sets the image fetching conditions and instructs the main scanning. As in the step S2901, the designated information including the kind of the film, the reading area (area designated by the user) and the reading resolution (resolution designated by the user), are transmitted to the firmware.
In a step S2911, the firmware of the system controller 2811 receives the reading conditions and executes the operations of the steps S2902 to S2908 under the conditions for the main scanning.
In a step S2912, the image data are transmitted to the external equipment 2810 and displayed by the software, and can be stored in another memory medium (such as hard disk, magnetooptical disk or floppy disk) of the external equipment 2810.
In the above-explained film scanner, the shading data are usually obtained in a state prior to the start of scanning, where the scanning motor is stopped and the light source is turned on. However, in the actual image reading operation, since the scanning motor is activated, the light amount distribution of the light source becomes different from that in reading the shading data because of the fluctuation of the power supply voltage resulting from the driving of the scanning motor. For this reason the exact correction of the shading has not been possible and the deterioration of the image quality has been unavoidable.
An object of the present invention is to provide an image reading apparatus capable of image reading of high quality.
Another object of the present invention is to provide an image reading apparatus capable of stable image reading.
The above-mentioned objects can be attained, according to an embodiment of the present invention, by an image reading apparatus comprising an image sensor for reading an image and outputting an image signal; movement means for causing a relative movement between the image sensor and the image; correction means for effecting shading correction on the image signal; and control means for controlling the movement means so as to effect movement with plural different moving speeds and causing the correction means to effect the shading correction on the image signal according to the plural moving speeds.
Such configuration enables to achieve stable image reading with high quality.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description, which is to be taken in conjunction with the appended drawings.